PubMed Health⌕ Search

Biomedical subjects

A K Samanta

Publications and source records attributed to A K Samanta.

At least 19 recordsLinked to original sources
PubMed2001

Regulation of chemokine receptor CCR5 and production of RANTES and MIP-1alpha by interferon-beta.

Trafficking of inflammatory T cells into the brain is associated with interactions of certain chemokines with their receptors, which plays an important role in the pathogenesis of multiple sclerosis (MS). We examined whether interferon-beta (IFN-beta) had the ability to regulate the production of chemokines and the expression of their receptors in T cells derived from patients with MS. It was demonstrated for the first time that in vitro exposure of T cells to IFN-beta-1a selectively inhibited mRNA expression for RANTES and MIP-1alpha and their receptor CCR5. T cell surface expression of CCR5 was significantly reduced in MS patients treated with IFN-beta, correlating with decreased T cell transmigration toward RANTES and MIP-1alpha. The study provides new evidence suggesting that IFN-beta treatment impairs chemokine-induced T cell trafficking by reducing the production of RANTES and MIP-1alpha and the expression of their receptors CCR5.

Adult↗
PubMed2000

Aberrant T cell migration toward RANTES and MIP-1 alpha in patients with multiple sclerosis. Overexpression of chemokine receptor CCR5.

Trafficking of inflammatory T cells into the central nervous system (CNS) plays an important role in the pathogenesis of multiple sclerosis. The directional migratory ability of peripheral T cells is associated with interactions of chemokines with their receptors expressed on T cells. In this study, transmigration of peripheral T cells toward a panel of chemokines was examined in patients with multiple sclerosis and healthy individuals using Boyden chemotactic transwells. A significantly increased migratory rate preferentially toward RANTES and MIP-1alpha, but not other chemokines, was found in T cells obtained from multiple sclerosis patients as opposed to healthy individuals (P: < 0.001). The migratory T-cell populations represented predominantly Th1/Th0 cells while non-migratory T cells were enriched for Th2-like cells. The study demonstrated further that aberrant migration of multiple sclerosis-derived T cells toward RANTES and MIP-1 alpha resulted from overexpression of their receptors (CCR5) and could be blocked by anti-CCR5 antibodies. These findings have important implications for our understanding of the mechanism underlying aberrant T cell trafficking in multiple sclerosis.

Cell Movement↗
PubMed1997

Hamycin inhibits IL-8-induced biologic response by modulating its receptor in human polymorphonuclear neutrophils.

IL-8, a neutrophil chemotactic agent, is involved in a large number of neutrophil-driven acute and chronic inflammatory diseases. We have found that hamycin, an antifungal agent, reduces IL-8-induced migration and binding of 125I-labeled IL-8 to neutrophils by 66 and 75%, respectively. Other IL-8-induced biologic functions, such as superoxide generation, intracellular Ca2+ mobilization, and enzyme release were also reduced in hamycin-treated cells by 50 to 75%. Anti-IL-8R Ab (C-X-CR1) and IL-8 itself failed to protect the cells from the effect of hamycin. Scatchard analysis of IL-8 binding data demonstrated that while the normal cells expressed 23,000 +/- 1,704 receptors/cell (Kd = 3.5 nM), the number was reduced to 8,000 +/- 592 receptors/cell (Kd = 3.43 nM) in hamycin-treated cells. Chemical cross-linking of 125I-labeled IL-8 to its receptor followed by 10% SDS-PAGE analysis and autoradiography showed that the signals in hamycin-treated cells were considerably reduced compared with those in controls. In the immunoblot, however, the signals in control and hamycin-treated cells were almost identical. The intensity of the fluorescence emission of diphenyl hexatriene at 430 nm and membrane microviscosity measured by diphenyl hexatriene were considerably reduced in hamycin-treated cells, resulting in a reduced number of functional IL-8R, presumably by conformational change in the receptor. The study suggests that hamycin may be a potent immunomodulator of the IL-8R for alleviation of inflammatory distress.

Adjuvants, Immunologic↗
PubMed1997

Binding of Escherichia coli heat-stable enterotoxin and rise of cyclic GMP in COLO 205 human colonic carcinoma cells.

Escherichia coli heat-stable enterotoxin (STa) was found to bind on the surface of human colonic (COLO 205) cells. The binding of [125I]STa to cell membranes was found to be specific, reversible and saturable. Scatchard analysis of the equilibrium binding demonstrated a single class of binding sites with a Kd of 0.5 x 10(-10) M. Autoradiographic analysis of polyacrylamide gel electrophoresis revealed the specific incorporation of [125I]STa into a single STa binding protein with a molecular mass of 95 kDa. Following incubation of COLO 205 cells with STa, a rise of intracellular cGMP was also evident.

Bacterial Toxins↗
PubMed1997

A Ca2+-dependent autoregulation of lipopolysaccharide-induced IL-8 receptor expression in human polymorphonuclear neutrophils.

IL-8, a potent neutrophil chemotactic agent, is known to be a key mediator in several inflammatory diseases. We found that 10 ng/ml of serum-activated LPS (Escherichia coli) efficiently up-regulated IL-8R on the surface of neutrophils within 30 min of LPS stimulation by 115 to 120% through de novo protein synthesis. After 30 min of LPS stimulation, reduction of IL-8R level was initiated and the normal level was restored within 2 h of LPS interaction. EDTA or EGTA and bestatin separately inhibited the receptor down-regulation by 98%, indicating the involvement of metalloprotease(s), more specifically an aminopeptidase in the process. Induction and subsequent reduction of IL-8 binding in serum-activated LPS-stimulated cells have been demonstrated in autoradiography. Intracellular Ca2+ level in these stimulated neutrophils was increased and decreased with alteration of IL-8R level. Although IL-8 binding was drastically reduced, the total IL-8R level, as detected by anti-IL-8R Ab measured by 125I-labeled anti-rabbit IgG, remained almost unaltered, indicating that minimal proteolysis occurred in IL-8R. Anti-IL-8R Ab and IL-8 itself could prevent this down-regulation significantly, suggesting that the susceptible epitope(s) might be in the IL-8 binding domain of the receptor. Under Ca2+-depleted conditions, the proteolysis was inhibited, which was accelerated upon addition of 1 mM of CaCl2. The study demonstrates that LPS-induced up-regulation of IL-8R leads to amplified IL-8-mediated biologic responses of neutrophils that are restored to normal level by activation of a Ca2+-dependent aminopeptidase. This may be useful for understanding the regulation of LPS-mediated inflammatory responses of neutrophils during bacterial infection.

Aminopeptidases↗
PubMed1997

Receptor-mediated endocytosis of IL-8: a fluorescent microscopic evidence and implication of the process in ligand-induced biological response in human neutrophils.

Interleukin 8 (IL-8), a neurophil-activating and chemotactic cytokine, is known to play a key role in the pathogenesis of a large number of neutrophil-driven inflammatory diseases. Although the cytokine is rapidly internalized at 37 degrees C with its receptors, there was no direct evidence for the ligand-induced endocytosis of the receptor or that of the interaction of receptor ligand complex at 37 degrees C. As a result, our understanding about the regulation of Il-8 induced biological response is very limited. In the present study, using FITC-IL-8 conjugate as a probe, we have demonstrated the time- and temperature-dependent endocytosis of IL-8 under fluorescent microscope. We have also shown that the bright fluorescent light on the surface of neutrophils gradually disappears and it becomes almost dark after 120 min of incubation. Monodansyl cadaverine (MDC, 900 microM), however, was found to retain the fluorescent light of FITC coupled with Il-8 on the cells. MDC and ouabain (2.5 mM) can inhibit the ligand induced endocytosis by 76% and 96%, respectively, compared to control. With respect to control, IL-8 induced biological responses e.g. IL-8 directed migration, intracellular Ca2+ release and superoxide release are significantly reduced by 77%, 94% and 76%, respectively, in presence of MDC. The study presents a direct visual evidence of the time and temperature-dependent receptor-mediated endocytosis of IL-8 which is inhibited by MDC and ouabain. This information is useful for understanding the ligand receptor interaction at 37 degrees C and may be useful for developing anti-inflammatory agents against IL-8.

Anions↗
PubMed1996

Dansyl cadaverine regulates ligand induced endocytosis of interleukin-8 receptor in human polymorphonuclear neutrophils.

Interleukin-8 (IL-8), a neutrophil chemotactic agent, acts as a key mediator in a large number of acute and chronic inflammatory diseases. At 37 degrees C, the receptor for IL-8 is rapidly internalized with its ligand. But no specific inhibitor of this ligand induced internalization of the receptor has been reported so far. We have found that monodansyl cadaverine (MDC) inhibited about 70% of IL-8 induced endocytosis and caused 70% and 66% inhibition of IL-8 mediated chemotaxis and respiratory burst response, respectively, in neutrophils. The uninternalized receptor was detected by anti IL-8R antibody in MDC treated cells. The endocytosis of IL-8R was strongly inhibited under Ca2+ depleted conditions which was restored on addition of 1 mM CaCl2 indicating the critical involvement of a Ca2+ ion in the process. Absence of receptor internalisation makes the MDC treated neutrophils suitable for studying the interaction of IL-8R with potential therapeutic agents e.g. for in vitro screening of anti-inflammatory agents.

Antigens, CD↗
PubMed1996

Identification and characterization of specific receptor for interleukin-8 from the surface of human monocytes.

A specific receptor for interleukin-8 has been identified on the surface of human monocytes using 125I IL-8 as a probe. A binding kinetic pattern shows that saturation was attained after 90 min and that the receptor was distinct from the receptors of other cytokines (IL-L alpha, IL-2, TNF alpha, GMCSF) and FMLP. Scatchard analysis of the binding data shows that 7000-10,000 receptors /monocyte are present with an equilibrium Kd 7 x 10(-9) M. By immunoblot, the receptor for IL-8 showed a sharp band with approximate M.W. 59 kD, consistent with the M.W. of IL-8 receptor of neutrophils. In Boyden Chamber, monocytes migrated towards IL-8 and the cytokine was observed to induce transient rise of intracellular Ca+2 in the cells. Thus, identification of functionally active IL-8 receptor in monocyte may be helpful for understanding its possible role during inflammation.

Antigens, CD↗
PubMed1995

Upregulation of interleukin-8 receptor in human polymorphonuclear neutrophils by formyl peptide and lipopolysaccharide.

Interleukin-8 (IL-8) is implicated in the pathogenesis of a large number of neutrophil-driven inflammatory diseases. Although the cytokine activates neutrophils through a receptor, no information is available regarding the regulation of IL-8 receptor (IL-8R) expression. The present study shows that, compared to control, the bacterial products--formylpeptide and LPS (serum-activated) upregulate IL-8 receptor by 54% and 115%, respectively, the former by degranulation of the secretory vesicle and the latter by de novo protein synthesis. The newly expressed IL-8R could be demonstrated with anti-IL-8R-antibody and by autoradiogram of the receptor crosslinked with [125I]IL-8. The study may be useful for understanding the potential role of IL-8 during neutrophil mediated inflammatory response.

Antibodies↗
PubMed1995

Regulation of interleukin-8 receptor expression in human polymorphonuclear neutrophils.

Interleukin-8, a neutrophil chemotactic agent, is known to have an active role in the induction of inflammatory response in a number of diseases. Although the activity of IL-8 is known to be through a receptor (IL-8R) on the surface of neutrophils, no information is available regarding the regulation of the IL-8R expression. The present study demonstrates that serum activated LPS at a concentration of 10 ng/ml induces expression of functionally active IL-8R by 120% within 30 min through de novo protein synthesis. The upregulated receptors could be detected by anti-IL-8R antibody and could also be demonstrated by autoradiography with crosslinking 125I IL-8. The serum-activated LPS-stimulated neutrophils migrated faster and showed higher Ca2+ flux over the unstimulated cells. The LPS-induced receptors were downregulated rapidly, about 85% of the receptor activity being lost within 90 min of incubation at 37 degrees C. The downregulation could be partially prevented by treatment with a cocktail of protease inhibitors, suggesting the possible involvement of protease(s) in this process. Both EDTA (100 microM) and bestatin (40 microM) afforded almost complete protection of the receptor from proteolytic cleavage indicating that the enzyme involved is a metalloprotease, possibly an aminopeptidase. The study shows that stimulation of PMNs with LPS leads to induction of IL-8R expression enhancing the IL-8-mediated biological responses and also provides evidence for post-stimulatory restoration of receptor level on the neutrophil surface by proteolytic cleavage of the amino-terminal end of the receptor.

Antigens, CD↗
PubMed1994

Ultrasonography of the tibialis posterior tendon in rheumatoid arthritis.

This work was carried out to assess the frequency of frank rupture of the tibialis posterior tendon (TPT) in RA and to determine if other pathology in the tendon can be correlated with foot deformity. Clinical, radiographic and ultrasonographic signs of TPT pathology were assessed bilaterally in 28 patients with RA and hindfoot involvement. The degree of hindfoot pain, the single-heel-rise test and the tibiocalcaneal angle were assessed clinically. The talometatarsal angle was measured on lateral weight-bearing radiographs. Tendon continuity and thickness were noted on sonography, both in the study group and in a control group of 14 patients. The TPT was significantly thinner in those rheumatoid patients with an abnormal single-heel-rise test when compared to those patients with a normal test (P < 0.001) and to the control group (P < 0.001). The mean thickness in patients with an abnormal test was 1.6 mm, in patients with a normal test it was 2.3 mm and in the controls it was 1.9 mm. In the rheumatoid group thinning of the tendon was significantly correlated (r = -0.33, P < 0.05) with heel valgus as assessed by the tibiocalcaneal angle. It was also significantly correlated (r = 0.31, P < 0.05) with pes planus as assessed by the talometatarsal angle. Only one case of frank rupture of the TPT was identified. There were also significant correlations between TPT thickness and patient age, disease duration and steroid therapy, such that tendon attenuation was associated with increasing age, longer disease and steroid usage. There was no association between TPT thickness and the degree of hindfoot pain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Functions of interleukin-8 are mediated through thiol group(s) of IL-8 receptor in human polymorphonuclear neutrophils. Effects of 5,5'-dithio-bis(2-nitrobenzoic acid) on IL-8 receptor.

Interleukin-8, a neutrophil chemotactic agent causes excessive accumulation of the cells in a number of inflammatory diseases. The activity has been shown to be mediated through a specific functional receptor present on the surface of neutrophils. No information is available about the amino acids constituting the IL-8 binding domain of the receptor. Treatment of neutrophils with 5,5'-dithio-bis(2-nitrobenzoic acid), a thiol-specific modifier, at the concentrations of 0.4 mM and 1 mM reduced IL-8 binding ability and IL-8-induced migration of the cells by 45% and 65%, respectively. Dithiothreitol could regenerate the binding capacity and the ligand could protect the receptor from the effect of the reagent. All the evidence suggests that one or more critical thiol residues are located in the IL-8 binding site of the receptor which are indispensible for normal functions of IL-8.

Chemotaxis↗
PubMed1993

Modification of sulfhydryl groups of interleukin-8 (IL-8) receptor impairs binding of IL-8 and IL-8-mediated chemotactic response of human polymorphonuclear neutrophils.

Interleukin-8 (IL-8), a monocyte-derived neutrophil chemotactic agent, has a potential role in the regulation of inflammatory responses. The specific receptor for IL-8 has been identified and characterized on the surface of human neutrophils (Samanta, A. K., Oppenheim, J. J., and Matsushima, K. (1989) J. Exp. Med. 169, 1185-1189). The present study demonstrates that at least two sulfhydryl groups of this receptor from human neutrophils participate in the binding of IL-8. Incubation of neutrophils with sulfhydryl group-modifying reagents, N-ethylmaleimide and diazene dicarboxylic acid bis-N,N-dimethylamide (diamide), severely impaired the binding of 125I-IL-8 to neutrophils. Treatment with 0.8 mM N-ethylmaleimide and 0.4 mM diamide inhibit binding of 125I-IL-8 to the neutrophils by 62 and 60%, respectively. These inhibitory effects could be reversed by 84-87% by treatment with 2-4 mM dithiothreitol. The saturable amount of the ligand, IL-8, provided partial protection against the modifying reagents. N-Ethylmaleimide and diamide at a concentration of 0.4 mM reduced chemotactic migration of neutrophils in a Boyden chamber by 95 and 60%, respectively. At a concentration of 0.4 mM, N-ethylmaleimide reduced the IL-8-induced (10 micrograms/ml) release of myeloperoxidase by 50%. Under identical conditions, 0.4 mM diamide could reduce release of myeloperoxidase by 63%. Finally, N-ethylmaleimide severely affected the overall binding and total uptake of 125I-IL-8 to the neutrophils at 37 degrees C, a condition required for receptor-mediated internalization of the ligand and recycling of the receptor to the surface of neutrophils. Nitro blue tetrazolium reduction test of the lipopolysaccharide-stimulated neutrophils indicates that compared to control general metabolic functions of thiol-modified cells were markedly retained. These data suggest that at least two conformationally vicinal free reactive sulfhydryl groups are located in the binding domain of the receptor in neutrophils which are essential for IL-8-mediated biological responses.

Binding Sites↗
PubMed1993

Disease variations in Asians in Leicester.

The epidemiological study of ethnic groups provides valuable information for physicians in a number of ways. First, it assists in the diagnostic approach in individual patients, especially for doctors unfamiliar with patients of a particular ethnic background. Second, it provides population data to assist in health care planning and provision for the present and future in districts where ethnic minorities are resident in significant numbers. Third, it may provide pointers for the study of pathogenic mechanisms. Fourth, changing epidemiology in migrant ethnic minorities may help to distinguish the degree of influence of genetic and environmental pathogenic factors. These studies are particularly valuable when minority populations are of a size which allows meaningful data to be collected on uncommon conditions. Furthermore the contrasts between migrant and indigenous populations are most clearly seen if migration has occurred over a restricted period. For these and other reasons the study of the migrant population from the Indian subcontinent (defined as India, Pakistan and Bangladesh) which has settled in Leicester since the mid-1960s has proved particularly rewarding. This report summarizes the distinctive epidemiological features of these people now living in Leicester.

Adult↗
PubMed1990

Interleukin 8 (monocyte-derived neutrophil chemotactic factor) dynamically regulates its own receptor expression on human neutrophils.

The regulation of monocyte-derived neutrophil chemotactic factor (MDNCF)/interleukin 8 (IL 8) receptor expression by the MDNCF/IL 8 ligand was examined using freshly isolated human peripheral blood neutrophils. MDNCF/IL 8 down-regulated greater than 90% of its own receptor expression within 10 min at 37 degrees C. This down-regulation was associated with internalization of the ligand. The radiolabeled MDNCF/IL 8 molecules after internalization were proteolytically degraded, and trichloroacetic acid-soluble molecules were released into the culture medium starting at 60 min. Lysosomotropic agents could inhibit this degradation of ligand suggesting the involvement of lysosomal enzymes in this proteolytic digestion. MDNCF/IL 8 receptors reappeared on the cell surface within 10 min after removal of free ligands from the culture medium. Cycloheximide did not alter the reappearance of the receptor suggesting that de novo protein synthesis of MDNCF/Il 8 receptors is not involved in this event and that receptors probably recycled. The addition of lysosomotropic agents partially inhibited the reappearance/recycling of the receptors, although none of these agents inhibited the binding of ligand to the surface receptors or ligand internalization. Ammonium chloride reduced the MDNCF/IL 8-induced neutrophil chemotactic response in a dose-dependent fashion. These data suggest that MDNCF/IL 8 receptor expression is dynamically regulated by MDNCF/IL 8 and that the rapid recycling of MDNCF/IL 8 receptors may be essential for the chemotactic response of neutrophils.

Ammonium Chloride↗
PubMed1990

The identification and quantitation of alkylated nucleobases by high-performance liquid chromatography with UV photodiode array detection.

The application of UV diode array detection in high-performance liquid chromatographic (HPLC) identification and quantitation of several classes of synthetic and commercially available alkylated nucleobases is investigated. Quantitative spectral overlays of these compounds to methyl standard references from a spectral library and absorbance ratios at two maximal wavelengths (lambda max) are found to be useful in categorizing the solutes. They can be grouped into classes of compounds originating from a specific nucleobase and classes of analogs having different alkyl substituents (e.g., methyl, ethyl, propyl, allyl, and benzyl) at the same position of the heterocycle. At a selected wavelength for alkylated nucleobases in the same class, the detector response factors are independent of the alkyl group (+/- 10%). This technique provides a practical means for both qualitative and quantitative analysis of product distribution of DNA base alkylation by using only readily obtainable methylated derivatives as the reference standards.

Adenine↗
PubMed1990

Enzyme immunoassay of testosterone using nitrocellulose discs as the solid phase.

An enzyme immunoassay (EIA) for the measurement of serum testosterone has been developed using nitrocellulose paper discs as the solid support. The paper discs (6 mm diameter) coated with testosterone-specific antibody were incubated with testosterone and testosterone-peroxidase conjugate in glass tubes. The amount of testosterone present in samples could be estimated from the bound peroxidase activity. The assay was validated by comparison with a microtitre plate-based ELISA and a commercial radioimmunoassay (RIA) kit. The correlation coefficient between RIA and EIA was 0.84. No significant cross reactivity was observed with other steroids, except for dihydrotestosterone. The inter- and intra-assay coefficients of variation were 4.4 and 9.6% respectively. The preservation and transport of the coated paper discs are convenient and the overall cost of the method is less than that of other methods.

Collodion↗